Our trip planning pretty much consists of a destination waypoint so I've not experienced any issues with route planning yet. However I did switch to custom Topo maps loaded on the SD card just fine, contrary to pre purchase research that turned up nothing to indicate it would even be possible to use Topo maps.
Attached pictures show the empty built in map and then switched to Topo map zoomed way out. The surrounding details and trails become increasingly more visible with closer zoom levels.
Quite happy with this discovery!
Axis 24.2 "was" tug'n a JK